Air-porous paper and process of making same



Patented Apr. 19, 1932 NITED STATES PATENT OFFICE- r FREDERICK RIEBEL, JR, TOLEDO, OHIO, ASSIGNOR TO AIR-WAY ELECTRIC .AI'PZI- ANGE CORPORATION, OF TOLEDO, OHIO, A CORPORATION OF DELAWARE AIR-POROUS PAPER. AND PROCESS OF MAKING SAME No Drawing. Application filed July 29, 1930. Serial No. 471,600.

In the development of the paper making art, it has been constantly endeavored to increase the closeness of fiber lay in the felted structure. Such type of structure, while leading in the direction of tensile strength, is diametrically opposed to porosity. On the other hand, where attention has been given to the development of a paper'structure capable of providing filtering interstices, as in the case of filter-paper making, the structure has lacked tensile strength. These respective properties of tensile strength and porosity havein fact constituted contradictory functions, as to direct the art along the lines of 1 the making of a product ofv good tensile strength and without porosity. Paper-having a structure providing high porosity for air, and yet at the same time having a high tensile strength, is accordingly a novel conception in the art, and one affording utilities along new and important lines.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the features hereinafter fully described,

and particularly pointed out in the claims,

the following description setting forth in detai-l certain illustrative embodiments of the invention, these being indicative however of but a few of the various ways in which the principle of the invention may be employed.

In its general aspects, the invention. contemplates the preparation of paper which is not only hi hly porous to air, at which is also of a high tensile strength at the same time.

"In the manufacture of. paper customarily, the pulped stock is treated in a beating ene, wlth prolonged heating to provide a iiient mass 1n the form of a suspension of the 40 fibers in water, the fibers being brought to a state of considerable isolation. The material is then treated in a Jordan engine for. further refining and breaking up of finer masses, such treatment conducing to a close lay and matting when subsequently run onto the forming wire. When well beaten and refined, the mass is supplied to the machine, a Fourdrinier machine. typically, and the shaking is adjusted to afford a maximum of close matting in the fiber lay. As the Fourdrinier wire passes over the suction boxes, a vacuum is applied to withdraw water, but gently so as to avoid opening up. the closely matted fiber structure. When dried, even though such paper be creped, where any. degree of tensile strength is shown, the structure is characterized by a closely laid fiber matting having very low porosity to air applied under pressure.v In fact, on application of air pressure to such paper, back pressure quickly builds up and rupture occurs.

Iiidirect contrast to this, my present invention contemplates the production of a paper.,,which has a high porosity to air flow,

and which at the same time has the contran5 dictory property of high tensile strength, The importance and utility of such a paper is particularly seen, when it is noted that it now -makes possible air bags for vacuum cleaners, protective diaphragms for air-venl0 tilated and cooled electric generators, motors, and other machinery where a considerable volume of air is to be supplied, without passing dust. I

'lhe'lower limit of porosity, in paper suit-. ?5 able -for use in the making of dust collecting bags for vacuum cleaners, is approximately 25 c.'f. m. (cubic feet of air per minute) of air flow under a pressure head represented by a pressure drop across a 11%" square sheet of the paper, read on a water manometer as 2",of pressure. i

It is understood that the above porosity requirement relates to the average -vacuum cleaner requirements and depends on the strength of the average vacuum cleaner blower. In other wonds, the stronger the blower, the more porosity a paper requires in order that it may not back up too much pressure against the blower and thereby'interfere with the suction producing capacity of the,blower.

As stock for the production of the present paper, I may primarily employ various materials, depending somewhat upon particular results in view, in general the fibers being of rather long character, for instance, rag stock, sulphite stock, sulphate stock, etc, preferably the latter for paper for quite high tensile strength. The stock, then instead of being thoroughly beaten and'Jordaned as in accordance with customary practice, is on the contrar very lightly beaten, just sufiicientorm an evenly flowing suspension, which is then run onto the forming wire, and felted, but with a relatively loose lay. The shaking'frames are desirably turned down from their adjustment to avoid the customary action. Or, in some cases I employ a machine having a very short shaking frame section. At the suction boxes, instead of the customary vacuum, I apply much more, two to four times as much, and disruptively open the interstices of the felted structure by means of such abrupt vacuum pull. The web is now preferably machine creped.

Prior to beating in the Jordan machine,

the stock is allowed to remain in suspension just long enough to reach an initial stage of hydration. The type of stock produced in the practice of my invention has characteristics of what is known as wild fiber stoek. This paper has a weight of not less than 30 .lbs. per ream and shows a fiber structure meshed to supply free interstices of a size to be impervious to particles the size of wheat flour, while being freely pervious to air without backing up pressure more than two inches as measured on a standard testing instrument providing a paper exposure eleven and threequarter inches square to the discharge of a blower fan whose static suction inlet capacity is 18 inches of water as measured by a manometer.

A sheet of such paper as applied to the air testing instrument noted, and then subjected to impacts from an impact device for determining sheet strength shows resistance against rupture by a 0.24 lb. wooden ball falling against the per endicular face ofthe sheet through as muc as a 36 in. arc (of 100 in. radius). If desired, more resistance to rupture may in fact also be had.

Such paper when made up into a bag with an opening fitting a vacuum cleaner mounting, when subjected to the discharge of a blower driven by an electric motor operating on a 110 volt circuit and capable of producing a sealed-ofi suction head of 18 in. of water as measured on a manometer, shows a vacuum of not less than 10 inches. If now the bag be loaded with 0.66 lb. of wheat flour,

test of a 0.24 lb. ball falling against the vertical surface of the bag through an arc of as much as 45 inches (on a 100 inch radius) there is no rupture. In fact, if desired the rupture-resistance may be much greater-than this.

As a further refinement of the invention, I

' may incorporate in the stock in the beating engine fibers of .cotton, hemp, jute, etc.,

chopped manila or hemp rope, and the like. These fibers disseminate in the pulp suspension, forming in the web product interlacing strengthening fibers, whereby the porosity standards above noted may be maintained, while still further increasing the tensile strength of the sheet.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention 1. An air-porous paper, having its fibers meshed to leave interstices impervious to particles the size of wheat flour, and transmitting air such as to occasion no more back pressure than about two inches against a blower forcin not less than substantially 25 cubic feet of air per minute through a 11 square sheet of such paper, and having a tensile strength under such pressure resisting impact of, an 0.24 lb. wooden ball falling through a 36 inch are having a radius of 100 inches.

2. An air-porous paper,'creped, and having its fibers meshed to leave interstices impervious to particles the size of wheat flour, and transmitting air such as to occasion no more'back pressure than about two inches against a blower forcing not less than substantially 25 cubic feet of air per minute through a.11% square sheet of such paper, and having a tensile strength under such. pressure resisting impact of an 0.24 lb. wooden ball falling through a 36 inch arc having a radius of 100 inches.

3. An air-porous paper, of sulphate stock, of weight not exceeding 30 lbs. per ream, and having its fibers meshed to leave interstices impervious to particles the size of wheat flour, and transmitting air such as to occasion no more back pressure than about two inches against a blower forcing not less than substantially 25 cubic feet of air per minute through a 11% square sheet of such paper, and having a tensile strength under such pressure resisting impact of an 0.24 lb. wooden ball falling through a 36 inch are having a radius of- 100 inches.

4. An air;porous paper, of sulphate stock, having its ulped structure including fibers of choppe rope, and meshed to leave interstices impervious to particles the size of wheat flour, and transmitting air such as to occasion no more back pressure than about two inches against a blower forcin not less than substantially 25 cubic feet 0? air per minute througha 11% square sheet of such paper, and having a tensile strength under such pressure resistin impact of an 0.24 lb. wooden ball falling t rough a 36 inch are having a radius of 100 inches.

essee? 

